Actuatable, occupant restraint systems, such as air bags, for vehicles are known in the art. Such restraint systems include one or more collision sensing devices for sensing vehicle crash acceleration (vehicle deceleration). Air bag restraint systems further include an electrically actuatable igniter, referred to as a squib. The collision sensing device may be an accelerometer that outputs an electrical signal having an electrical characteristic indicative of the crash event. A monitoring circuit analyzes the electrical output signals from the accelerometer and makes a determination if a deployment crash event is occurring. If a deployment crash event is determined to be occurring, an electrical current is passed through the squib to ignite the squib. When ignited, the squib initiates the flow of inflation fluid into an air bag from a source of inflation fluid, as is known in the art.
The monitoring circuit connected to the accelerometer is often a controller, such as a microcomputer, which performs a crash algorithm on the acceleration signal for the purpose of discriminating between a deployment event and a non-deployment crash event. When a deployment crash event is determined to be occurring, the restraint is actuated, e.g., an air bag is deployed.
Many types of crash algorithms for discriminating between deployment and non-deployment crash events are known in the art. Algorithms typically are adapted to detect particular types of crash events for particular vehicle platforms. One example of such an algorithm is taught in U.S. Pat. No. 5,587,906 to McIver et al. and assigned to TRW Inc.
Air bag restraint systems may require more than one sensor for detection of a deployment crash event. For example, plural sensors may be arranged in a voting scheme in which all the sensors must “agree” that a deployment crash event is occurring before restraint actuation is initiated. In such an arrangement, the second sensor is referred to as a “safing sensor.” Air bag actuation occurs only if the first sensor and the safing sensor indicate a deployment crash event is occurring.
If a single sensor is used, a “safing function” can be achieved by a single controller performing two algorithms on the crash acceleration signal, one being designated as the discrimination algorithm and one being designated as the safing algorithm. If both algorithm determinations agree that a deployment crash event is occurring, the restraint is actuated. As an alternative, the single controller could perform two algorithms on acceleration signals from two separate accelerometer outputs.